The present invention relates to a distributed system and to a process for acquiring remote data in packets with a communication protocol optimizing the transmission speed. These system and process are applicable in the automotive industry for quickly and effectively controlling certain operation parameters or functions in a vehicle through a single time-shared bus.
Different data processing and communications systems applied to vehicles are known in the state of the art.
European patent number 0653856, to Regie Nationale des Usines Renault, S.A., discloses a process and device for evaluating the quality of a communication network assembled in an automotive system and comprises several electronic modules connected by means of a communication bus and which emit each one of the signals in the form of frames composed of high and low binary states. A measurement is taken of the transaction time difference between said high and low binary states on each signal frame circulating in the bus for a constant tension difference representative of this transition and set by the features of the bus. Said measurement is carried out by means of one or several particular bits located outside of the frame arbitration area. A maximum time difference is sought and compared with a predefined maximum value for a configuration of the vehicle.
European patent number 0681383, to Regie Nationale des Usines Renault, S.A., discloses a process for transmitting messages between modules of a communication network connected by a bus, such that the frame emitter module defines a field in the identifier of addresses of each frame; it initializes the content of the field of the first frame to be emitted with a value known by all recipient modules; it increases the content of the field; it modulates its maximum value in each frame emission; and such that each receptor module accepts the frame after a filtering by comparison of one part of said field with a memorized model and by comparison between the identifier field of the frame and one or several indicators memorized in view of its use in the application of the module. This process is applied to a communication network assembled in an automotive vehicle.
U.S. Pat. No. 5,697,048, to Pioneer Electronic Corporation, discloses a data communication system assembled in a vehicle provided with at least one master unit, a plurality of slave units and a communication bus. Each one of the slave units is provided with a first recipient device for receiving communication data transmitted through the communication bus; a first assessment device to evaluate whether the first recipient device has failed in the reception of the data or not; and a first transmission device to transmit recognition data to indicate a failure in the reception of the first recipient device in case the first assessment device has assessed that a reception failure has occurred. The master unit is provided with a second transmission device to transmit communication data emitted to the slave units; a second recipient device to receive the transmitted recognition data; a second assessment device to assess whether the data corresponding to the transmitted communication data have been received by the second recipient device; and a process control device to carry out a certain process to face the failure of the first recipient device. The system is prepared for being used in a component network of an audio-visual (AV) system in the vehicle.
European patent number 0849122, by Temic Telefunken Microelectronic GMbH, discloses a process for transmitting digital data from a central unit and several control modules connected thereto such that they are suitable for the communication of control information, especially for controlling safety devices in an automobile, through a bus system. When a critical state is detected from the safety point of view, the control information contains suitable orders warning of said critical safety state, using a first transmission protocol in which the central unit emits the control information to those units corresponding to the control modules. In critical safety cases, the data transmission speed increases, activating a second transmission protocol, which does not provide any re-emission of control information, it is therefore shorter than the first protocol.
The present invention proposes a distributed system and a process for acquiring remote data in packets with a communication protocol, especially characterized by optimizing the transmission speed, being particularly applicable to the follow-up and control of the values of signals provided by a series of transducer devices distributed in different parts of an automotive vehicle, and which follow different analog or digital variables. These variables can correspond to vehicle operation parameters or functions, such as tire pressure and temperature, engine lubricating oil pressure and temperature, battery charge and voltage level, temperatures in different elements or areas of the vehicle, status of switches, ABS equipment, stereo equipment, speech or sound emission signals with the possibility of echo canceling, etc.
The system of the present invention comprises a digital processing unit associated to a combined master or main circuit and slave or subordinate circuits system, both provided with digital processors, connected to each other through a single, time-shared communications serial bus. Each one of said slave circuits is associated to a transceiver device. The master circuit is provided to perform, upon petition of an activation by said digital processing unit, a repetitive or non-repetitive communication with each one of the slave circuits, during which communication a bit frame circulates through said time-shared serial bus according to a transmission protocol formed by a series of bits packets separated by a short time interval.
Each one of said packets associated to a corresponding slave circuit comprises:
a start bit, which has a longer duration or length than the data bits, so that they can be fully identified; a delay/synchronism bit for the frames going from master to slave; one or more (according to the number of slave devices present in the system) address bits indicating the slave device to be consulted; and several data bits containing information sent to/or coming from each slave device.
The information from the slave circuits is stored in said master circuit in arrayed entries containing said data bits, which are susceptible to be acquired sequentially by the digital processing unit through a parallel bus and upon the petition of a reading order from said digital processing unit, while the repetitive master circuit communication with the slave circuit continues for carrying out a new consultation cycle. In turn, the digital processing unit is linked to a bus of the vehicle, such as a CAN or other type of bus.
An essential feature of the present invention is that, in order to maximally increase the data acquisition and processing speed, the protocol does not incorporate any transmission/reception error correction routine, although it preferably includes an error detection bit, therefore the system simply skips over the detected errors, going on to the reading of the following data packet. In other words, the system gives priority to the acquisition of a new data packet from a certain slave circuit over the integral (or corrected) recovery of a preceding data packet which has undergone an error in the transmission/reception thereof. This is possible due to the high transmission frequency in the data packet flow, such that the unexpected loss of one of them is not a significant disturbance for controlling the parameter involved.
The system uses the Manchester format to encode each bit of the bit packets. In each bit packet, the length of said start bit is at least two times the length of each one of the data bits of the packet, whereas the delay/synchronism bit length is at least 1.5 times the length of one of said data bits. The start bit is provided for generating a reinitialization of all the slave circuits. Preferably, each bit packet further includes an additional protocol error detection bit in the last place of the data field or address field. Each bit packet optionally contains, in addition to the address bit or bits, data bits sent to the slave device, being transmitted such that they are univocally recognized by the slave device.
The system only admits digital form signals, therefore, when one of said transducer devices provides an analog signal, as is the case, for example, in a fuel tank level transducer, the transducer is then associated to an analog/digital converter connected to the corresponding slave circuit.